Plasma actuated cascade flow vectoring

ABSTRACT

A system for directing airflow, a gas turbine engine, and a method for directing airflow exiting a cascade of internal airfoils are provided. An exemplary system for directing airflow includes a cascade of internal structures spanning an airflow path. Each of the internal structures includes a rounded trailing edge. The system further includes at least one plasma generating device positioned on the rounded trailing edge of each internal structure. Also, the system includes a controller configured to selectively energize and de-energize each plasma generating device to selectively alter a direction of local airflow around each internal structure to produce a combined airflow exiting the cascade in a desired direction.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally tomethods, systems and apparatuses for selectively directing airflow in aninternal cascade of airfoils. More particularly, embodiments of thesubject matter relate to methods, systems and apparatuses using actuatedplasma to produce a combined airflow exiting a cascade of internalairfoils in a desired direction.

BACKGROUND

Gas turbine engines typically comprise an air-compressor-forming sectionfeeding a combustion chamber that produces hot gases to drive theturbine stages downstream. The engine compressor comprises a pluralityof moving bladed disks, separated by successive stages of statorcascades of vanes that redirect the airflow. Conventional vanes aregenerally variable-pitch vanes. The angular position of a variable-pitchvane about its pivotable radial axis can be selectively adjusted inorder to improve compressor efficiency. The variable-pitch vanes areoriented using a mechanism known as a variable-pitch mechanism or a VSVwhich stands for variable stator vane. There are various designs of suchmechanisms, but on the whole, they all comprise one or more actuatorsfixed to the engine casing, synchronization bars or a control shaft,rings surrounding the engine and positioned transversely with respect tothe axis thereof, and substantially axial levers also known as pitchcontrol rods, connecting the rings to each of the variable-pitch vanes.The actuators rotate the rings about the engine axis and these cause allthe levers to turn synchronously about the vane pivots.

These mechanisms are subjected both to the aerodynamic loads applied tothe vanes, which are high, and to loads resulting from friction in thevarious connections. Further, the mechanisms themselves limit the designof stator cascades of vanes, as clearances are necessary to allow forpivoting the vanes.

It would be desirable to selectively adjust the direction of airflowexiting a stator cascade of vanes without the use of variable-pitchvanes. Further, it would be desirable to obviate the structuralrequirements of variable-pitch vanes. The use of fixed vanes thatprovide for control of airflow direction from a cascade of internalvanes could provide for increased performance and reduced mechanicalcomplexity.

Hence, there is a need for a method, system and apparatus forselectively directing airflow around internal airfoils. Use of actuatedplasma to produce a combined airflow exiting a cascade of internalairfoils would provide for improved cascade performance and durability.Other desirable features and characteristics of the method, system andapparatus will become apparent from the subsequent detailed descriptionand the appended claims, taken in conjunction with the accompanyingdrawings and the preceding background.

BRIEF SUMMARY

A system for directing airflow, a gas turbine engine, and a method fordirecting airflow exiting a cascade of internal airfoils are provided.In an exemplary embodiment, the system for directing airflow includes acascade of internal structures spanning an airflow path. Each of theinternal structures includes a rounded trailing edge. The system furtherincludes at least one plasma generating device positioned on the roundedtrailing edge of each internal structure. Also, the system includes acontroller configured to selectively energize and de-energize eachplasma generating device to selectively alter a direction of localairflow around each internal structure to produce a combined airflowexiting the cascade in a desired direction.

A gas turbine engine is also provided. The gas turbine engine includes acascade of internal airfoils. Each of the internal airfoils includes afirst surface and an opposite second surface connected at a roundedtrailing edge. A first single dielectric barrier discharge plasmaactuator is positioned on the first surface and the rounded trailingedge of each of the internal airfoils. Also, a second single dielectricbarrier discharge plasma actuator is positioned on the second surfaceand the rounded trailing edge of each of the internal airfoils. Eachfirst single dielectric barrier discharge plasma actuator and eachsecond single dielectric barrier discharge plasma actuator areselectively energized and de-energized to selectively alter a directionof local airflow around each of the internal airfoils to produce acombined airflow exiting the cascade in a desired direction.

Also provided is a method for directing airflow exiting a cascade ofinternal airfoils. The method includes coupling a first plasmagenerating device on a first surface and a rounded trailing edge of eachof the internal airfoils, and coupling a second plasma generating deviceon an opposite second surface and the rounded trailing edge of each ofthe internal airfoils. Also, the method includes selectively energizingthe first plasma generating device and the second plasma generatingdevice on each of the internal airfoils to produce a plasma and toselectively alter a direction of local airflow around each of theinternal airfoils to produce a combined airflow exiting the cascade in adesired direction.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures and wherein:

FIG. 1 is a schematic illustration of an example single dielectricbarrier discharge plasma actuator for use in a cascade of internalstructures in accordance with various embodiments herein;

FIG. 2 is a longitudinal-sectional view of an example gas turbine engineincluding a cascade of internal structures for use with the plasmaactuator of FIG. 1;

FIG. 3 is an enlarged longitudinal-sectional view of the example gasturbine engine of FIG. 2, including a portion of an example cascade ofinternal structures in accordance with various embodiments herein;

FIG. 4 is a partial view of an internal structure of FIG. 3, includingan example arrangement of plasma actuators in accordance with variousembodiments herein;

FIG. 5 is a partial view of an exemplary internal structure, includingan alternate arrangement of plasma actuators in accordance with variousembodiments herein;

FIG. 6 is a partial view of an exemplary internal structure, includingan alternate arrangement of plasma actuators in accordance with variousembodiments herein;

FIG. 7 is an example illustration of a steady actuation signal and anunsteady actuation signal; and

FIG. 8 is schematic of an example actuator circuit for energizing thesingle dielectric barrier discharge plasma actuator of FIG. 1.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

As described above, controlling the direction of an airflow exiting acascade of internal structures, such as airfoils, is provided throughselective plasma actuation. Specifically, plasma generating devices arelocated on trailing edges of internal structures to selectively alter adirection of local airflow around each of the internal structures toproduce a combined airflow exiting the cascade in a desired direction.The plasma generating devices can be flush mounted into the structures,producing little or no effect on the flow when not in use, i.e., whenturned “off.”

Further, as contemplated herein, fixed internal structures are able toselectively adjust the direction of an airflow exiting a cascade ofinternal structures through the use of plasma actuators. Specifically,the fixed internal structures electrically control local airflow, ratherthan providing mechanical control of airflow through pivoting or movingthe structures as in conventional methods.

It will be appreciated that while the disclosed examples are directed toa compressor for a gas turbine engine utilizing an internal cascade ofairfoils, the disclosed methods, systems and apparatuses may be utilizedto provide flow control to any suitable device including an internalcascade of structures in an airflow path.

Referring to FIG. 1, a plasma generating device 10 is illustrated. Theexemplary plasma generating device 10 is a single dielectric barrierdischarge (SDBD) plasma actuator. As shown in FIG. 1, the plasmaactuator 10 includes an exposed electrode 20 and an enclosed electrode22 separated by a dielectric barrier material 24. The electrodes 20, 22and the dielectric barrier material 24 may be mounted, for example, to asubstrate 26. A power supply 28, such as a high voltage AC power supply,is electrically coupled to the plasma actuator 10. Specifically, thepower supply 28 is electrically coupled to the electrodes 20, 22.Further, the power supply 28 is connected to a controller 29 thatdirects the power supply 28 to selectively energize or de-energize theplasma actuator 10.

It will be understood that the exposed electrode 20 may be at leastpartially covered, while the enclosed electrode may be at leastpartially exposed. During operation, when the controller 29 causes thepower supply to provide an applied AC voltage with a sufficientamplitude, the air surrounding the plasma actuator 10 will locallyionize in the region of the largest electric field (i.e. potentialgradient) forming a plasma 30. The plasma 30 generally forms at an edge21 of the exposed electrode 20. Further, the plasma actuator 10 createsa strong electric field that draws ionized particles toward the plasmaactuator 10. As a result, selectively energizing and de-energizing theplasma actuator 10 can modify the behavior of local airflow around theplasma actuator 10. The ability to tailor the actuator-induced flow bythe arrangement of the plasma actuator 10 on airfoils allows one toachieve a wide variety of actuation strategies for cascades of internalairfoils as described below.

In the present disclosure, surface mounted SDBD plasma actuators 10 areused to alter the direction of airflow exiting an internal cascade ofairfoils by active means. The plasma actuators 10 may be flush mountedto the airfoils, producing little or no effect on flow through theinternal cascade when not actuated. In other words, the internal cascadewill not cause a loss in design operating point efficiency. Furthermore,the plasma actuators may be implemented in an open or closed loop forcontrol of the airflow exiting the internal cascade. An example openloop implementation energizes or de-energizes the plasma actuator basedupon the corrected speed and corrected flow direction exiting theinternal cascade. An example closed loop implementation utilizes asensor or sensors 32 to monitor the internal cascade aerodynamics,synthesizing a stability state variable. Each plasma actuator 10 isselectively energized or de-energized to increase or decrease attractionof local airflow toward the plasma actuator 10. As a result, a boundaryseparation location of the local airflow relative to the airfoil onwhich the plasma actuator is mounted is adjusted, resulting in a changein the exit angle of the airflow relative to the airfoil.

Referring now to FIG. 2, an example gas turbine engine 160 is shown. Thegas turbine engine 160 generally includes a housing 110, a fan 120 whichreceives ambient air 122, a compressor section 123 including a lowpressure compressor 124 and a high pressure compressor 126, a combustionchamber 130, a high pressure turbine 132, a low pressure turbine 134,and a nozzle 136 from which combustion gases are discharged from the gasturbine engine 160. The high pressure turbine 132 is joined to the highpressure compressor 126 by a high pressure shaft or rotor 140, while thelow pressure turbine 134 is joined to both the low pressure compressor124 and the fan 120 by a low pressure shaft 142. The low pressure shaft142 is at least in part rotatably disposed co-axially with and radiallyinwardly of the high pressure shaft 140. In FIG. 2, the compressorsection 123 of the gas turbine engine 160 includes a compressor statorcascade 152.

FIG. 3 is a simplified cross sectional schematic of the compressorstator cascade 152. As shown, the compressor stator cascade 152 includesa plurality of internal structures 154, such as airfoils. Each structure154 extends radially (substantially perpendicular to the plane of thedrawing) from a hub to a tip across an airflow path. When shaped like anairfoil, each internal structure 154 extends axially from a leading edge162 to a trailing edge 164. Further, each structure 154 includes a firstsurface 172 and a second surface 174. As shown, air, indicated by arrow180, enters the cascade 152 and is directed by the internal structures154 to produce a combined airflow, depicted by one of arrows 182,exiting the cascade 152 in a desired direction, i.e., at a desired exitangle with respect to the cascade 152. While FIG. 3 illustrates eachstructure 154 as an airfoil, it is noted that such cross-sectional shapeis not required. Rather, each structure 154 need only be provided with arounded trailing edge 164, and may have any desired cross sectionalshape suitable for use in directing the airflow.

FIG. 4 illustrates the mounting of plasma actuators 10 on an exemplarystructure 154 of FIG. 3. As shown, a plasma actuator 10 is mounted flushon the first surface 172 at the rounded trailing edge 164 of thestructure 154. Further, a plasma actuator 10 is mounted flush on theopposite second surface 174 at the rounded trailing edge 164. While onlytwo plasma actuators 10 are shown mounted on the exemplary structure154, it is contemplated that more than two be utilized for eachstructure 154. Further, it will be understood, however, that the plasmaactuators 10 may be strategically placed anywhere along the structure154, and in any arrangement. Each plasma actuator 10 may extend from thehub to the tip of the structure 154.

Cross-referencing FIGS. 1 and 4, one of the electrodes 22 is embeddedwithin the structure 154, while the other electrode 20 is mountedgenerally flush with or just below the surface of structure 154. In thisconfiguration, when an AC electric field if applied, the plasma 30 formson the respective surface of the structure 154.

As shown in FIG. 4, the typical local airflow represented by arrows 190moves along the surfaces 172, 174. Typically, such airflow wouldcontinue in the direction of arrows 192, separating from the structure154 at an exemplary boundary separation location 194. However, uponselective energizing of the plasma actuators 10, the ionization of airand the creation of an electric field causes the air to flow in thedirection of arrows 200. As a result, a new boundary separation location202 is established toward the trailing edge 164 of the structure 154.

Further, each plasma actuator 10 may be independently and selectivelyenergized to provide a desired exit angle of local airflow from theexemplary structure 154. For example, the plasma actuator 10 on thesurface 172 may be energized while the plasma actuator 10 on the surface174 is de-energized. As a result, the airflow above surface 172 mayfollow arrow 200, while the airflow below surface 174 may follow arrow192. In combination, such selective actuation may result in airflowexiting the airfoil in the direction of arrow 210. Likewise,de-energizing the plasma actuator 10 on the surface 172 while energizingthe plasma actuator 10 on the surface 174 causes the airflow abovesurface 172 to follow arrow 192, while the airflow below surface 174 mayfollow arrow 200. In combination, such selective actuation may result inairflow exiting the airfoil in the direction of arrow 212.

In addition to the preceding binary example, the plasma actuators 10 maybe operated at varying selected voltages to provide degrees ofattraction of airflow toward either surface 172, 174, allowing for theselection of a tailored exit angle of airflow from the structure 154.Further, coordination of the plasma actuators 10 on all of the internalstructures 154 in the cascade 152 provides for the selection of acombined airflow exiting the cascade 152 at a desired direction.

FIG. 5 illustrates the mounting of plasma actuators 10 on an alternateinternal structure 154. The internal structure 154 includes a roundedtrailing edge 164 having a first side 220 and a second side 222. Theinternal structure 154 may not have the cross-sectional shape of aconventional airfoil. Rather, the internal structure need only have arounded trailing edge 164. As used herein a “rounded” edge includesthose having circular cross sections, as well as non-circular crosssections such as elliptical cross sections. As shown, two plasmaactuators 230 are mounted on the first side 220 of the rounded trailingedge 164 and two plasma actuators 232 are mounted on the second side 222of the rounded trailing edge 164. Of course, the embodiment of FIG. 5may include one or more plasma actuators 230 on the first side 220 andno plasma actuators 232 on the second side 222. Further, the arrangementselected for a particular internal structure 154, i.e., zero plasmaactuators, one plasma actuator, or more than one plasma actuator oneither side, need not be selected for each internal structure 154 in thecascade. Rather, the selected arrangement provides for redirecting localairflow represented by arrows 190 from flowing in the direction ofarrows 192 to flow in the direction of arrows 200, and to move theboundary separation location upon selective energizing of the plasmaactuators as discussed above.

FIG. 6 illustrates an alternate internal structure 154. As shown, theexemplary internal structure 154 includes a rounded trailing edge 164that forms a point 240. Specifically, the first side 220 is rounded andthe second side 222 is rounded, but the first side 220 and the secondside 222 intersect at point 240. As used herein, a “rounded” edgeincludes those having rounded portions that intersect at a point. Asshown, two plasma actuators 230 are mounted on the first side 220 of therounded trailing edge 164 while no plasma actuators are mounted on thesecond side 222 of the rounded trailing edge 164. Of course, theembodiment of FIG. 6 may include one or more plasma actuators 232 on thesecond side 222 and no plasma actuators 230 on the first side 220.Further, the arrangement selected for a particular internal structure154, i.e., zero plasma actuators, one plasma actuator, or more than oneplasma actuator on either side, need not be selected for each internalstructure 154 in the cascade. Rather, the selected arrangement providesfor redirecting local airflow represented by arrows 190 from flowing inthe direction of arrows 192 to flow in the direction of arrows 200, andto move the boundary separation location upon selective energizing ofthe plasma actuators as discussed above.

The example SDBD plasma actuator 10 utilizes an AC voltage power supply28 for its sustenance. However, if the time scale associated with the ACsignal driving the formation of the plasma 30 is sufficiently small inrelation to any relevant time scales for the flow, the associated bodyforce produced by the plasma 30 may be considered effectively steady.However, unsteady actuation may also be applied and in certaincircumstances may pose distinct advantages. Signals for steady versusunsteady actuation are contrasted in FIG. 7. In the illustrated example,an example steady actuation signal 700 in comparison with an unsteadyactuation signal 710. Both the steady actuation signal 700 and theunsteady actuation signal 710 utilize the same high frequency sinusoid.Referring to the figure, it is apparent that with regard to the unsteadyactuation signal 710, during time interval T₁ the plasma actuator 10 ison only during the sub-interval T₂. Hence, the signal sent to the plasmaactuator 10 has a characteristic frequency of f=1/T₁ that will be muchlower than that of the sinusoid and will comparable to some relevantfrequency of the particular flow that one wishes to control. Inaddition, an associated duty cycle T₂/T₁ may be defined. It will beunderstood that the frequency and duty cycle may be independentlycontrolled for a given flow control application as desired.

FIG. 8 shows a sample circuit 800 used to create the high-frequency,high-amplitude AC voltage generated by the AC voltage power supply 28.In this example, a low amplitude, sinusoidal waveform signal isgenerated by a signal generator 802. The generated signal is supplied toa power amplifier 804. The amplified voltage is then fed through anadjustment module 806 into the primary coil of a transformer 810. Thehigh voltage output for the excitation of the plasma actuators 10 isobtained from the secondary coil of the transformer 810.

As noted above, the example plasma actuator 10 may be implemented in anopen or closed loop for control of rotating stall. An example open loopimplementation utilizes a controller 29 operatively coupled to the ACvoltage power supply 28 to energize or de-energize the plasma actuator10 based upon the corrected speed and corrected mass flow of thecompressor. An example closed loop implementation utilizes a sensor 32mounted proximate the trailing edge of the cascade 152 to monitor theaerodynamics of airflow exiting the cascade. The exemplary sensor 32 isoperatively coupled to the controller 29 to synthesize a stability statevariable. In either implementation, the controller 29 selectivelyenergizes or de-energizes each plasma actuator 10 on each structure 154modify the local airflow around each structure 154.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

What is claimed is:
 1. A system for directing airflow comprising: acascade of internal structures spanning an airflow path, wherein each ofthe internal structures includes a rounded trailing edge; at least oneplasma generating device positioned on the rounded trailing edge of eachinternal structure; and a controller configured to selectively energizeand de-energize each plasma generating device to selectively alter adirection of local airflow around each internal structure to produce acombined airflow exiting the cascade in a desired direction.
 2. Thesystem of claim 1 wherein each plasma generating device is a singledielectric barrier discharge plasma actuator, wherein each internalstructure has two sides, and wherein each internal structure is providedwith more than one plasma actuator on each side.
 3. The system of claim1 wherein each plasma generating device is a single dielectric barrierdischarge plasma actuator, wherein each internal structure has twosides, and wherein each internal structure is provided with at least oneplasma actuator on one side and no plasma actuators on the other side.4. The system of claim 1 wherein the controller is configured toenergize each plasma generating device on a selected internal airfoil tomove a boundary separation location of the local airflow around theselected internal structure toward the trailing edge of the selectedinternal structure.
 5. The system of claim 1 wherein each plasmagenerating device is flush with the respective internal structure. 6.The system of claim 1 wherein each internal structure extends radiallyfrom a hub to a tip, and wherein each first plasma generating deviceextends from the hub to the tip of the respective internal structure. 7.The system of claim 1 further comprising a sensor to monitor theaerodynamics of the combined airflow exiting the cascade.
 8. The systemof claim 7 wherein the sensor is operatively coupled to the controllerto selectively energize and de-energize each plasma generating device.9. A gas turbine engine comprising: a cascade of internal airfoils,wherein each of the internal airfoils includes a first surface and anopposite second surface connected at a rounded trailing edge; a firstsingle dielectric barrier discharge plasma actuator positioned on thefirst surface and the rounded trailing edge of each of the internalairfoils; and a second single dielectric barrier discharge plasmaactuator positioned on the second surface and the rounded trailing edgeof each of the internal airfoils, wherein each first single dielectricbarrier discharge plasma actuator and each second single dielectricbarrier discharge plasma actuator are selectively energized andde-energized to selectively alter a direction of local airflow aroundeach of the internal airfoils to produce a combined airflow exiting thecascade in a desired direction.
 10. The gas turbine engine of claim 9further comprising a controller configured to selectively energize andde-energize each first single dielectric barrier discharge plasmaactuator and each second single dielectric barrier discharge plasmaactuator.
 11. The gas turbine engine of claim 10 wherein the controlleris configured to energize the first plasma actuator and the secondplasma actuator on a selected internal airfoil to move a boundaryseparation location of the local airflow around the selected internalairfoil toward the trailing edge of the selected internal airfoil. 12.The gas turbine engine of claim 9 further comprising a power supplyelectrically coupled to the first plasma actuator and the second plasmaactuator on each of the internal airfoils.
 13. The gas turbine engine ofclaim 9 wherein the first plasma actuator is flush with the firstsurface and the rounded trailing edge of each respective internalairfoil, and wherein each second plasma actuator is flush with thesecond surface and the rounded trailing edge of each respective internalairfoil.
 14. The gas turbine engine of claim 9 wherein each internalairfoil extends radially from a hub to a tip, and wherein the firstplasma actuator and the second plasma actuator extend from the hub tothe tip of each internal airfoil.
 15. The gas turbine engine of claim 9further comprising a sensor to monitor the aerodynamics of the combinedairflow exiting the cascade.
 16. The gas turbine engine of claim 15wherein the sensor is operatively coupled to the controller to cause thepower supply to selectively energize and de-energize the first plasmaactuator and the second plasma actuator on a selected internal airfoil.17. A method for directing airflow exiting a cascade of internalairfoils comprising: coupling a first plasma generating device on afirst surface and a rounded trailing edge of each of the internalairfoils; coupling a second plasma generating device on an oppositesecond surface and the rounded trailing edge of each of the internalairfoils; and selectively energizing the first plasma generating deviceand the second plasma generating device on each of the internal airfoilsto produce a plasma and to selectively alter a direction of localairflow around each of the internal airfoils to produce a combinedairflow exiting the cascade in a desired direction.
 18. The method ofclaim 17 wherein selectively energizing the first plasma generatingdevice and the second plasma generating device on each of the internalairfoils moves a boundary separation location of the local airflowaround each of the internal airfoils toward the trailing edge of each ofthe internal airfoils.
 19. The method of claim 18 further comprisingmonitoring the aerodynamics of the combined airflow exiting the cascade.20. The method of claim 19 further comprising selectively de-energizingthe first plasma generating device and the second plasma generatingdevice on each of the internal airfoils in response to the monitoredaerodynamics of the combined airflow exiting the cascade to alter thecombined airflow exiting the cascade.